Model for Predicting Impact of Development On Florida Keys Should Be Revised

WASHINGTON -- Decision-makers should not rely on a proposed computer model that is part of a multimillion-dollar study to determine the ability of the Florida Keys ecosystem to withstand further development, says a new report from the National Academies' National Research Council. Although the overall model in its current form would provide misleading results, some components could be revised to supply a limited assessment of the impact.

"The task of creating a model to predict the impact of all future development was perhaps too ambitious an undertaking considering the lack of available data," said Scott Nixon, professor of oceanography, University of Rhode Island, Narragansett, and chair of the committee that wrote the report. "Incomplete and outdated information, coupled with inaccurate assumptions, makes the model -- as it stands now -- inappropriate for drawing conclusions about the impact of future development."

The model, known as the Carrying Capacity Analysis Model, is being prepared in conjunction with the Florida Keys Carrying Capacity Study, a state initiative to measure how much land development the Keys can support without additional damage to its natural resources and local infrastructure. The state project is being overseen by the Florida Department of Community Affairs and the U.S. Army Corps of Engineers, which hired the URS Corp. to develop the model. The two agencies asked the Research Council to review the contractor's efforts to date.

The committee first commented on the initial plans for the model in a preliminary report early last year, and was given a "complete first draft" of the model to review last November. Although the contractor was generally responsive to concerns raised in the preliminary report, several fundamental problems remain in the draft model, the committee's new report says. For example, the model does not adequately account for the impact of tourism on the islands; makes unrealistic assumptions about hurricane evacuation; fails to evaluate how shifts in population would affect the Keys; and does not address the effects of growth and tourism on water quality and the coastal marine environment. In addition, census data from 1990 instead of 2000 were used, leading to errors that resonate throughout the model.

The committee applauded the model's user-friendly computer interface, which allows the input of different scenarios for land-use changes, such as new housing developments, redevelopment of urban areas, and restoration of disturbed land. However, the interface does not offer sufficient flexibility for users to specify other parameters such as changes in the average number of people in a household, or in the number of residents and tourists, which fluctuates with the seasons.

In addition to the user interface, the model is composed of six modules that, in theory, should work together to evaluate the impact of further development on the Keys. Three of the modules representing fiscal issues, municipal water concerns, and terrestrial impacts should -- with some relatively minor technical adjustments -- prove useful in estimating some of the effects of development on the Keys, provided they are used with caution and expert judgment, the committee said. The marine module should not be used without thorough revision, and the socioeconomic module and the hurricane evacuation component of the human infrastructure module should not be used without major revisions.

On the whole, the model's output implies a precision that simply does not exist, the committee said. For example, almost none of the individual modules that contribute to the overall model is "calibrated" to actual historical values. Because models are highly simplified representations of the real world, they must be adjusted, or calibrated, based on past real-life conditions. However, this was either not done, or modules were calibrated to conditions in other areas, which may not be representative of the Keys. Furthermore, the model does not include any sensitivity testing, which is used to measure the confidence in a model's predictions. Any display of the model's results should reflect and describe its inherent uncertainties.

The Florida Keys are a string of small islands extending southwest from the southern tip of the state. They are the third largest barrier reef ecosystem in the world. Given their ecologically rich and environmentally sensitive nature, the Keys were designated "an area of critical state concern" by the Florida government in 1974.

The Research Council study was sponsored by the U.S. Army Corps of Engineers and Florida Department of Community Affairs. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.Read the full text of A Review of the Florida Keys Carrying Capacity Studyfor free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web site or by calling (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).